Nickel-based ultrafine powder

ABSTRACT

In order to reduce the size of a laminated ceramic capacitor by reducing the thickness of a dielectric material, to increase the number of laminated dielectric layers and electrodes, and to elevate the capacity, the quantity of coarse particles of which particle diameters exceed 1 μpm is reduced from the metal powder used in the internal electrodes. There is provided a nickel-based ultra-fine powder, wherein the average particle diameter of primary particles is 0.05 to 0.3 μm, the number of the primary particles that have a particle diameter of 1 μm or larger is 50 ppm or less relative to the total number of the particles, and the number of the primary particles that have a particle diameter of 0.6 times or smaller than the average particle diameter is 10% or less relative to the total number of the particles. The nickel-based ultra-fine powder is produced from nickel chloride vapor or the like using a vapor-phase hydrogen reduction method.

TECHNICAL FIELD

The present invention relates to a nickel-based ultra-fine powder usedmainly in the internal electrode of a multilayer ceramic capacitor.

In the present invention, the nickel-based ultra-fine powder means anickel ultra-fine powder and a nickel alloy ultra-fine powder. Thenickel ultra-fine powder means an ultra-fine powder of pure nickel ornickel that contains unavoidable impurities; and a nickel alloy means analloy that contains nickel as the major component to which an alloycomponent is added, and for example, a nickel alloy that contains asmall quantity of Mn, Si and the like, or an alloy of nickel and a metaleasily alloyed with nickel, such as Zr, W, Cu, Cr, Fe or Al. As thenickel alloy for the internal electrode of a multilayer ceramiccapacitor, the alloy that contains 95% or more by mass of nickel ispreferred.

BACKGROUND ART

For nickel ultra-fine powder used in the internal electrode of amultilayer ceramic capacitor, with the reduction of the thickness ofinternal electrodes and dielectric layers, it is important to reduce thequantity of coarse particles in order to avoid the defect due to theshort-circuiting between electrodes.

There has been a technique to reduce the average particle diameter ofnickel ultra-fine powder to 0.2 to 0.6 μm, and to reduce the existenceprobability of course particles that have particle diameters of 2.5times or larger than the average particle diameter in term of number to0.1% (1000 ppm) or less (see for example, Patent Document 1).

There has also been a technique to reduce the average particle diameterof nickel ultra-fine powder to 0.1 to 1.0 μm, and to reduce theexistence probability of course particles that have particle diametersof 2 μm or larger in term of number to 700/one million (700 ppm) or less(see for example, Patent Document 2).

Furthermore, there has been disclosed a nickel powder wherein theaverage diameter of primary particles is 0.1 to 2 μm, the number ofparticles that have particle diameters of 1.5 times or larger than theaverage particle diameter in the laser diffraction scattering particlesize distribution measurement is 20% or less of the total particlenumber, and the number of particles that have particle diameters of 0.5times or smaller than the average particle diameter is 5% or less of thetotal particle number (see for example, Patent Document 3).

[Patent Document 1] Japanese Patent Laid-Open No. 11-189801

[Patent Document 2] Japanese Patent Laid-Open No. 2001-73007

[Patent Document 3] Japanese Patent Laid-Open No. 2001-247903

DISCLOSURE OF THE INVENTION

Heretofore, the thickness of an internal electrode and the thickness ofa dielectric material in a multilayer ceramic capacitor was 1 μm ormore, for example, the thickness of an internal electrode was 1.5 μm,and the thickness of a dielectric material was 3 μm. Therefore,conventional nickel ultra-fine powder used as the internal electrode ofa multilayer ceramic capacitor had a large average particle diameter anda wide particle size distribution, the particle diameters of coarseparticles that were allowed to be mixed incidentally were also large,and the incidental mixing probability of the coarse particles was alsohigher than that in the current situation. In recent years, however, theinternal electrode and the dielectric material tend to be thinned to 1μm or thinner to reduce the size of the multilayer ceramic capacitor;and the layers of laminated dielectric materials and internal electrodestend to be increased in number to elevate the capacity of the capacitor.

Therefore, the average particle diameter of the primary particles of themetal powder used in the internal electrode must be smaller than 1 μm,and it is essential that the quantity of the coarse particles ofparticle diameter that exceeds 1 μm is limited to a certain level andreduce the percentage of short-circuiting caused by metal particles thatthrust through the dielectric material between electrodes. If thequantity of fine particles that have particle diameters of 0.6 times orsmaller than the average particle diameter is large, since theseparticles cause oxidizing expansion or low-temperature sintering easierthan particles of the average particle diameter, there is possibility ofcausing the dielectric material to crack during the process for firingthe multilayer ceramic capacitor.

An object of the present invention is to provide a nickel-basedultra-fine powder wherein the above-described problems are solved.

In order to solve the above-described problems, the present inventionprovides a nickel-based ultra-fine powder, wherein the average particlediameter of primary particles is 0.05 to 0.3 μm, the number of theprimary particles that have a particle diameter of 1 μm or larger is 50ppm or less relative to the total number of the particles, and thenumber of the primary particles that have a particle diameter of 0.6times or smaller than the average particle diameter is 10% or lessrelative to the total number of the particles.

According to the present invention, there is exerted an effect that therejection rate in manufacturing small or high-capacity laminated ceramiccapacitors with the thickness of the dielectric material and theinternal electrode being 1 μm or less is extremely lowered.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, a primary particle means a particle whereinthe contour of a single particle can be distinguished when a powder inthe state of dry particles is observed through a scanning electronmicroscope (SEM). When the powder is not dispersed in a solvent, theprimary particles are often present in an aggregated form. Whendispersed under adequate conditions in a liquid such as an organicsolvent, aggregation is loosened, and primary particles can be presentseparately.

In order to confirm that the number of primary particles that have aparticle diameter of 1 μm or larger is 50 ppm of the total number ofparticles or less, the total number of primary particles observedthrough a SEM must be 200,000 or more. In order to confirm that thenumber of primary particles that have a particle diameter of 0.6 timesor smaller than the average particle diameter is 10% or less of thetotal number of particles, the total number of primary particlesobserved through a SEM must be 4,000 or more.

In the present invention, the reason why the average particle diameterof a primary particle is 0.3 μm or smaller is that if it exceeds 0.3 μm,the short-circuiting rate of internal electrodes is significantlyincreased. If the number of particles that can be lined in the directionof the thickness of the internal electrode is large, it is consideredthat a continuous electrode is formed after firing.

It is extremely difficult to obtain powder whose average particlediameter is 0.3 μm or smaller and whose number of particles that haveparticle diameters of 1 μm or larger is 50 ppm or less of the totalnumber of particles by classifying powder that has a particle sizedistribution wherein the average particle diameter of a primary particleexceeds 0.3 μm.

The reason why the average particle diameter of a primary particle is0.05 μm or larger is that, when a nickel powder paste is prepared and anelectrode is formed by printing, the nickel powder can be sufficientlydispersed in the paste. If the particle diameter is excessively smallcausing firm aggregation, when the nickel powder is dispersed in asolvent to prepare the paste, it becomes difficult to loosen aggregationand disperse the powder.

The reason why the number of particles wherein the particle diameter ofprimary particles is 1 μm or larger is 50 ppm or less of the totalnumber of particles is to restrict the rate of short-circuiting of theelectrodes caused by coarse particles to a practically acceptable level,the coarse particle having particle diameters of larger than 1 μm whichthrust through the dielectric material between electrodes.

The reason why the number of primary particles that have particlediameters of 0.6 times or smaller than the average particle diameter isdecided to be 10% or less of the total number of particles is asfollows: Fine particles are oxidized and expand easier than relativelylarge particles of particle diameters near the average particlediameter, and start sintering from a relatively low temperature.Therefore, if the number of fine particles of particle diameters of 0.6times or smaller than the average particle diameter exceeds 10%, strainis generated in the dielectric material during sintering in the firingprocess for manufacturing a multilayer ceramic capacitor causingcracking. The reason is to prevent this.

It is preferable that the nickel-based ultra-fine powder is manufacturedfrom a nickel chloride vapor using a vapor phase hydrogen reductionmethod, because the particle size is even, and the particle shape isnearly spherical. The thus manufactured nickel-based ultra-fine powderis most suitable for the use in a multilayer ceramic capacitor.

The present invention will be described below in further detailreferring to examples and comparative examples.

EXAMPLE 1

Three kinds of gases, which were a gas produced by subliming nickelchloride, hydrogen gas, and nitrogen gas, were mixed so that the moleratio of the gas produced by subliming nickel chloride became 0.10, andnickel powder was manufactured by the vapor-phase reaction in a reactioncolumn heated to 1000 to 1100° C. Image analysis was performed for 4000particles of the obtained nickel powder using the SEM, and the flow rateof the mixed gas in the reaction column was adjusted so that the averageparticle diameter of primary particles became 0.2 μm.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter of primary particleswas 0.21 μm, and the number of primary particles that had particlediameters of 0.12 μm (0.6 times the average particle diameter) or lesswas 4% of the total number of observed particles. The number of primaryparticles that had particle diameters of 1 μm or larger observed for512,000 particles in a lowered magnification of the SEM was 258 ppm ofthe total number of observed particles.

A water slurry was prepared from nickel powder obtained by vapor-phasereaction, the nickel powder was sufficiently dispersed in water using adispersing machine equipped with an ultrasonic vibrator, and then theslurry was classified using an imperforate-wall basket-type centrifugalseparator with a skimming pipe (internal capacity: 3 L, basket innerdiameter: 300 mm, water slurry supply rate: 2.5 L/min, rotation speed:1800 rpm), and water slurry discharged from the skimming pipe wascollected. The water slurry contained nickel powder from which coarseparticles had been removed. The collected slurry was pressure dehydratedand vacuum dried to recover the nickel powder.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter of primary particleswas 0.20 μm, and the number of primary particles that had particlediameters of 0.12 μm (0.6 times the average particle diameter) or lesswas 4% of the total number of observed particles. The number of primaryparticles that had particle diameters of 1 μm or larger counted for512,000 particles in a lowered magnification of the SEM was 4 ppm of thetotal number of observed particles.

EXAMPLE 2

A water slurry was prepared from nickel powder obtained by vapor-phasereaction in Example 1, the nickel powder was sufficiently dispersed inwater using a dispersing machine equipped with an ultrasonic vibrator,and then the slurry was classified using an imperforate-wall basket-typecentrifugal separator with a skimming pipe (internal capacity: 3 L,basket inner diameter: 300 mm, water slurry supply rate: 2.5 L/min,rotation speed: 1400 rpm), and water slurry discharged from the skimmingpipe, specifically, the water slurry contained nickel powder from whichcoarse particles had been removed, was collected. The collected slurrywas pressure dehydrated and vacuum dried to recover the nickel powder.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter of primary particleswas 0.20 μm, and the number of primary particles that had particlediameters of 0.12 μm (0.6 times the average particle diameter) or lesswas 4% of the total number of observed particles. The number of primaryparticles that had particle diameters of 1 μm or larger counted for512,000 particles in a lowered magnification of the SEM was 44 ppm ofthe total number of observed particles.

EXAMPLE 3

Three kinds of gases, which were a gas produced by subliming nickelchloride, hydrogen gas, and nitrogen gas, were mixed so that the moleratio of the gas produced by subliming nickel chloride became 0.17, andnickel powder was manufactured by the vapor-phase reaction in a reactioncolumn heated to 1000 to 1100° C. Image analysis was performed for 4000particles of the obtained nickel powder using the SEM, and the flow rateof the mixed gas in the reaction column was adjusted so that the averageparticle diameter of primary particles became 0.3 μm.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter of primary particleswas 0.27 μm, and the number of primary particles that had particlediameters of 0.16 μm (0.6 times the average particle diameter) or lesswas 9% of the total number of observed particles. The number of primaryparticles that had particle diameters of 1 μm or larger observed for512,000 particles in a lowered magnification of the SEM was 721 ppm ofthe total number of observed particles.

A water slurry was prepared from nickel powder obtained by vapor-phasereaction, the nickel powder was sufficiently dispersed in water using adispersing machine equipped with an ultrasonic vibrator, and then theslurry was classified using an imperforate-wall basket-type centrifugalseparator with a skimming pipe (internal capacity: 3 L, basket innerdiameter: 300 mm, water slurry supply rate: 2.5 L/min, rotation speed:1600 rpm), and water slurry discharged from the skimming pipe,specifically, the water slurry contained nickel powder from which coarseparticles had been removed, was collected. The collected slurry waspressure dehydrated and vacuum dried to recover the nickel powder.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter of primary particleswas 0.26 μm, and the number of primary particles that had particlediameters of 0.16 μm (0.6 times the average particle diameter) or lesswas 9% of the total number of observed particles. The number of primaryparticles that had particle diameters of 1 μm or larger counted for512,000 particles in a lowered magnification of the SEM was 37 ppm ofthe total number of observed particles.

EXAMPLE 4

Three kinds of gases, which were a gas produced by subliming nickelchloride, hydrogen gas, and nitrogen gas, were mixed so that the moleratio of the gas produced by subliming nickel chloride became 0.10, agas produced by subliming zirconium chloride was further added in aquantity of 0.5% by mass relative to the gas produced by sublimingnickel chloride, and nickel-zirconium alloy powder was manufactured bythe vapor-phase reaction in a reaction column heated to 1000 to 1100° C.

Image analysis was performed for 4000 particles of the obtainednickel-zirconium alloy powder using the SEM, and the flow rate of themixed gas in the reaction column was adjusted so that the averageparticle diameter of primary particles became 0.2 μm. As a result ofimage analysis for 4000 particles of the obtained nickel-zirconium alloypowder using the SEM, the average particle diameter of primary particleswas 0.20 μm, and the number of primary particles that had particlediameters of 0.12 μm (0.6 times the average particle diameter) was 5% ofthe total number of observed particles. The number of primary particlesthat had particle diameters of 1 μm or larger observed for 512,000particles in a lowered magnification of the SEM was 392 ppm of the totalnumber of observed particles.

A water slurry was prepared from nickel-zirconium alloy powder obtainedby vapor-phase reaction, the nickel-zirconium alloy powder wassufficiently dispersed in water using a dispersing machine equipped withan ultrasonic vibrator, and then the slurry was classified using animperforate-wall basket-type centrifugal separator with a skimming pipe(internal capacity: 3 L, basket inner diameter: 300 mm, water slurrysupply rate: 2.5 L/min, rotation speed: 1500 rpm), and water slurrydischarged from the skimming pipe, specifically, the water slurrycontained nickel-zirconium alloy powder from which coarse particles hadbeen removed, was collected. The collected slurry was pressuredehydrated and vacuum dried to recover the nickel-zirconium alloypowder.

As a result of image analysis for 4000 particles of the obtainednickel-zirconium alloy powder using the SEM, the average particlediameter of primary particles was 0.20 μm, and the number of primaryparticles that had particle diameters of 0.12 μm (0.6 times the averageparticle diameter) or less was 5% of the total number of observedparticles. The number of primary particles that had particle diametersof 1 μm or larger counted for 512,000 particles in a loweredmagnification of the SEM was 39 ppm of the total number of observedparticles.

EXAMPLE 5

Three kinds of gases, which were a gas produced by subliming nickelchloride, hydrogen gas, and nitrogen gas, were mixed so that the moleratio of the gas produced by subliming nickel chloride became 0.10, agas produced by subliming tungsten chloride was further added in aquantity of 0.5% by mass relative to the gas produced by sublimingnickel chloride, and nickel-tungsten alloy powder was manufactured bythe vapor-phase reaction in a reaction column heated to 1000 to 1100° C.

Image analysis was performed for 4000 particles of the obtainednickel-tungsten alloy powder using the SEM, and the flow rate of themixed gas in the reaction column was adjusted so that the averageparticle diameter of primary particles became 0.2 μm. As a result ofimage analysis for 4000 particles of the obtained nickel-tungsten alloypowder using the SEM, the average particle diameter of primary particleswas 0.22 μm, and the number of primary particles that had particlediameters of 0.13 μm (0.6 times the average particle diameter) or lesswas 5% of the total number of observed particles. The number of primaryparticles that had particle diameters of 1 μm or larger observed for512,000 particles in a lowered magnification of the SEM was 407 ppm ofthe total number of observed particles.

A water slurry was prepared from nickel-tungsten alloy powder obtainedby vapor-phase reaction, the nickel-tungsten alloy powder wassufficiently dispersed in water using a dispersing machine equipped withan ultrasonic vibrator, and then the slurry was classified using animperforate-wall basket-type centrifugal separator with a skimming pipe(internal capacity: 3 L, basket inner diameter: 300 mm, water slurrysupply rate: 2.5 L/min, rotation speed: 1500 rpm), and water slurrydischarged from the skimming pipe, specifically, the water slurrycontained nickel-tungsten alloy powder from which coarse particles hadbeen removed, was collected. The collected slurry was pressuredehydrated and vacuum dried to recover the nickel-tungsten alloy powder.

As a result of image analysis for 4000 particles of the obtainednickel-tungsten alloy powder using the SEM, the average particlediameter of primary particles was 0.21 μm, and the number of primaryparticles that had particle diameters of 0.13 μm (0.6 times the averageparticle diameter) or less was 5% of the total number of observedparticles. The number of primary particles that had particle diametersof 1 μm or larger counted for 512,000 particles in a loweredmagnification of the SEM was 46 ppm of the total number of observedparticles.

Comparative Example 1

A water slurry was prepared from nickel powder obtained by vapor-phasereaction in Example 1, the slurry was classified using animperforate-wall basket-type centrifugal separator with a skimming pipe(internal capacity: 3 L, basket inner diameter: 300 mm, water slurrysupply rate: 2.5 L/min, rotation speed: 1300 rpm), and water slurrydischarged from the skimming pipe, specifically, the water slurry thatcontained nickel powder from which coarse particles had been removed wascollected. The collected slurry was pressure dehydrated and vacuum driedto recover the nickel powder.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter of primary particleswas 0.20 μm, and the number of primary particles that had particlediameters of 0.12 μm (0.6 times the average particle diameter) or lesswas 4% of the total number of observed particles. The number of primaryparticles that had particle diameters of 1 μm or larger counted for512,000 particles in a lowered magnification of the SEM was 54 ppm ofthe total number of observed particles.

Comparative Example 2

A water slurry was prepared from nickel powder obtained by vapor-phasereaction in Example 1, the slurry was classified using animperforate-wall basket-type centrifugal separator with a skimming pipe(internal capacity: 3 L, basket inner diameter: 300 mm, water slurrysupply rate: 2.5 L/min, rotation speed: 1000 rpm), and water slurrydischarged from the skimming pipe, specifically, the water slurry thatcontained nickel powder from which coarse particles had been removed wascollected. The collected slurry was pressure dehydrated and vacuum driedto collect the nickel powder.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter was 0.20 μm, and thenumber of primary particles that had particle diameters of 0.12 μm (0.6times the average particle diameter) or less was 4% of the total numberof observed particles. The number of primary particles that had particlediameters of 1 μm or larger counted for 512,000 particles in a loweredmagnification of the SEM was 173 ppm of the total number of observedparticles.

Comparative Example 3

Three kinds of gases, which were a gas produced by subliming nickelchloride, hydrogen gas, and nitrogen gas, were mixed so that the moleratio of the gas produced by subliming nickel chloride became 0.18, andnickel powder was manufactured by the vapor-phase reaction in a reactioncolumn heated to 1000 to 1100° C.

Image analysis was performed for 4000 particles of the obtained nickelpowder using the SEM, and the flow rate of the mixed gas in the reactioncolumn was adjusted so that the average particle diameter of primaryparticles became 0.32 μm. As a result of image analysis for 4000particles of the obtained nickel powder using the SEM, the averageparticle diameter of primary particles was 0.34 μm, and the number ofprimary particles that had particle diameters of 0.20 μm (0.6 times theaverage particle diameter) or less was 10% of the total number ofobserved particles. The number of primary particles that had particlediameters of 1 μm or larger counted for 512,000 particles in a loweredmagnification of the SEM was 1926 ppm of the total number of observedparticles.

A water slurry was prepared from nickel powder obtained by vapor-phasereaction, the nickel powder was sufficiently dispersed in water using adispersing machine equipped with an ultrasonic vibrator, and then theslurry was classified using an imperforate-wall basket-type centrifugalseparator with a skimming pipe (internal capacity: 3 L, basket innerdiameter: 300 mm, water slurry supply rate: 2.5 L/min, rotation speed:1600 rpm), and water slurry discharged from the skimming pipe,specifically, the water slurry that contained nickel powder from whichcoarse particles had been removed was collected. The collected slurrywas pressure dehydrated and vacuum dried to recover the nickel powder.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter of primary particleswas 0.32 μm, and the number of primary particles that had particlediameters of 0.19 μm (0.6 times the average particle diameter) or lesswas 10% of the total number of observed particles. The number of primaryparticles that had particle diameters of 1 μm or larger counted for512,000 particles in a lowered magnification of the SEM was 92 ppm ofthe total number of observed particles.

Comparative Example 4

Three kinds of gases, which were a gas produced by subliming nickelchloride, hydrogen gas, and nitrogen gas, were mixed so that the moleratio of the gas produced by subliming nickel chloride became 0.08, andnickel powder was manufactured by the vapor-phase reaction in a reactioncolumn heated to 1000 to 1100° C. Image analysis was performed for 4000particles of the obtained nickel powder using the SEM, and the flow rateof the mixed gas in the reaction column was adjusted so that the averageparticle diameter of primary particles became 0.10 μm.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter of primary particleswas 0.11 μm. As a result of image analysis for 4000 particles of thenickel powder obtained by mixing the above nickel powder with the nickelpowder obtained by the vapor-phase reaction in Example 1 using the SEM,the average particle diameter of primary particles was 0.20 μm and thenumber of primary particles that had particle diameters of 0.12 μm (0.6times the average particle diameter) or less was 19% of the total numberof observed particles. The number of primary particles that had particlediameters of 1 μm or larger observed for 512,000 particles in a loweredmagnification of the SEM was 219 ppm of the total number of observedparticles.

A water slurry was prepared from this nickel powder, the nickel powderwas sufficiently dispersed in water using a dispersing machine equippedwith an ultrasonic vibrator, and then the slurry was classified using animperforate-wall basket-type centrifugal separator with a skimming pipe(internal capacity: 3 L, basket inner diameter: 300 mm, water slurrysupply rate: 2.5 L/min, rotation speed: 1800 rpm), and water slurrydischarged from the skimming pipe, specifically, the water slurry thatcontained nickel powder from which coarse particles had been removed wascollected. The collected slurry was pressure dehydrated and vacuum driedto recover the nickel powder.

As a result of image analysis for 4000 particles of the obtained nickelpowder using the SEM, the average particle diameter of primary particleswas 0.20 μm, and the number of primary particles that had particlediameters of 0.12 μm (0.6 times the average particle diameter) or lesswas 19% of the total number of observed particles. The number of primaryparticles that had particle diameters of 1 μm or larger counted for512,000 particles in a lowered magnification of the SEM was 3 ppm of thetotal number of observed particles.

A paste for an internal electrode was prepared using nickel-basedultra-fine powders of Examples 1 to 5 and Comparative Examples 1 to 4,and multilayer ceramic capacitors were fabricated to compare failurerates due to short-circuiting and cracking. After printing the paste ofnickel powder or nickel alloy powder on green sheets that had adielectric material of a thickness of about 1.2 μm so that the thicknessbecame about 1.2 μm, 100 layers were stuck, pressure bonded, cut andprocessed by a binder-removing process and a firing process. As theresults shown in Table 1, a multilayer ceramic capacitor using nickelpowder or nickel alloy powder according to the examples of the presentinvention has a significantly low short-circuiting rate of internalelectrodes and occurrence rate of internal cracking compared withcomparative examples. TABLE 1 Percentage Average Number ratio of short-Percentage particle particles of average Number ratio of circuiting ofoccurrence diameter particle diameter × particles of 1 μm internal ofinternal (μm) 0.6 or less (%) or larger (ppm) electrode (%) cracks (%)Example 1 0.20 4 4 7 0 Example 2 0.20 4 44 9 0 Example 3 0.26 9 37 8 0Example 4 0.20 5 39 8 0 Example 5 0.21 5 46 10 0 Comparative 0.20 4 5415 0 Example 1 Comparative 0.20 4 173 95 0 Example 2 Comparative 0.32 1092 28 0 Example 3 Comparative 0.20 19 3 6 51 Example 4

1. A nickel-based ultra-fine powder, wherein the average particlediameter of primary particles is 0.05 to 0.3 μm, the number of theprimary particles that have a particle diameter of 1 μm or larger is 50ppm or less relative to the total number of the particles, and thenumber of the primary particles that have a particle diameter of 0.6times or smaller than the average particle diameter is 10% or lessrelative to the total number of the particles.
 2. The nickel-basedultra-fine powder according to claim 1, wherein the nickel-basedultra-fine powder is produced from nickel chloride vapor using avapor-phase hydrogen reduction method.
 3. The nickel-based ultra-finepowder according to claim 1, wherein the nickel-based ultra-fine powderis used for a multilayer ceramic capacitor.
 4. The nickel-basedultra-fine powder according to claim 2, wherein the nickel-basedultra-fine powder is used for a multilayer ceramic capacitor.